1. Field of the Invention
The present invention relates to an improvement of a toroidal continuously variable transmission which is used as a transmission unit constituting an automatic transmission apparatus for a vehicle or as a transmission for adjusting the operation speeds of various kinds of industrial machines such as a pump. Specifically, the present invention provides a structure in which a plurality of concave grooves (fine grooves) are formed in both a peripheral of a power roller and a one-side surface of a disk in an axial direction in order to improve a traction coefficient of a rolling contact area between the axially one-side surface and the peripheral surface of the power roller while ensuring durability of the disk and the power roller. Further, the present invention provides such the concave grooves with low cost.
2. Description of Related Art
In some field, a toroidal continuously variable transmission is generally used as a transmission apparatus for a vehicle. FIGS. 9 and 10 show a basic configuration of the toroidal continuously variable transmission which is currently put to practical use. This toroidal continuously variable transmission is called as a double cavity type in which a pair of input-side disks 1 and 1 are rotatably supported to an input rotary shaft 2 while being concentric and interlocked with each other in a state that input-side inner surfaces 3 and 3 corresponding to one-side surfaces in an axial direction, which are formed into a toroidal curve surface (a circular-arc concave surface in a sectional view) and are opposed to each other.
In addition, an output cylinder 5 having an output gear 4 fixedly attached to an outer circumferential surface of a center portion thereof is supported to a position around a center portion of the input rotary shaft 2 so as to be rotatable about the input rotary shaft 2. Output-side disks 6 and 6 are supported to both end portions of the output cylinder 5 by a spline-engagement so as to be rotatable together with the output cylinder 5. In this state, output-side inner surfaces 7 and 7 of both the output-side disks 6 and 6 corresponding to one-side surfaces in the axial direction, which are formed into a toroidal curve surface, are opposed to both the input-side inner surfaces 3 and 3.
Two power rollers 8 and 8 having a spherical convex surface are disposed in a space (cavity) between both the input-side inner surface 3 and the output-side inner surface 7 around the input rotary shaft 2. The power rollers 8 and 8 are supported to inner surfaces of trunnions 9 and 9 through support shafts 10 and 10 each having a base half portion and a front half portion which are eccentric with each other and a plurality of rolling bearings so as to be rotatable in a direction of the front half portions of the support shafts 10 and 10 and be slightly swingable about the base half portions of the support shafts 10 and 10. The trunnions 9 and 9 are swingable about tilting shafts 11 and 11 which are provided at both end portions of the trunnions 9 and 9 in a longitudinal direction (an inside and outside direction in FIG. 9 and a vertical direction in FIG. 10) so as to be concentric with each other.
An operation in which the trunnions 9 and 9 swing (inclining) is carried out by displacing the trunnions 9 and 9 in the axial direction of the tilting shafts 11 and 11 by hydraulic actuators 12 and 12. That is, when a speed needs to be changed, the trunnions 9 and 9 are displaced in the axial direction of the tilting shafts 11 and 11 by pressure oil supplied to the actuators 12 and 12. As a result, a direction of a force acting in a direction perpendicular to the rolling contact area between the peripheral surfaces of the power rollers 8 and 8 and the input-side and output-side inner surfaces 3 and 7 is changed (side slip occurs), and then the trunnions 9 and 9 are displaced while swinging about the tilting shafts 11 and 11.
At the time of operating the toroidal continuously variable transmission described above, the input-side disk 1 on one side (on the left side in FIG. 9) is driven to rotate by a drive shaft 13 through a loading cam press unit 14. As a result, the pair of input-side disks 1 and 1 supported to both end portions of the input rotary shaft 2 rotate together while being pressed in a direction to be close to each other. Then, the rotation is transmitted to both the output-side disks 6 and 6 through the power rollers 8 and 8 and then is extracted from the output gear 4.
The operations at the time of changing a rotation speed ratio between the input rotary shaft 2 and the output gear 4 will be explained.
When a deceleration is carried out between the input rotary shaft 2 and the output gear 4, the trunnions 9 and 9 swing to a position shown in FIG. 9, and then the peripheral surfaces of the power rollers 8 and 8 are brought into direct contact with the center portions of the input-side inner surfaces 3 and 3 of the input-side disks 1 and 1 and the outer circumferential portions of the output-side inner surfaces 7 and 7 of both the output-side disks 6 and 6, respectively.
On the contrary, when an acceleration is carried out, the trunnions 9 and 9 swing in a direction opposite to that shown in FIG. 9, and then the peripheral surfaces of the power rollers 8 and 8 are brought into direct contact with the outer circumferential portions of the input-side inner surfaces 3 and 3 of both the input-side disks 1 and 1 and the center portions of the output-side inner surfaces 7 and 7 of both the output disks 6 and 6.
When the swing angle of the trunnions 9 and 9 is set to an intermediate value, it is possible to obtain an intermediate speed ratio between the input rotary shaft 2 and the output gear 4.
At the time of operating the toroidal continuously variable transmission described above, in the rolling contact area (traction area) between the peripheral surfaces of the power rollers 8 and 8 and the input-side and output-side inner surfaces 3 and 7 of the input-side and output-side disks 1 and 6, a power is transmitted through a traction oil. Here, a friction coefficient (traction coefficient) of the traction oil is a constant value, and it is necessary to apply a large pressing force to the rolling contact area in order to transmit a large torque in the rolling contact area.
However, when applying such a large pressing force, durability of the input-side and output-side disks 1 and 6 or the power rollers 8 and 8 may deteriorate. In addition, in order to ensure strength of the disks 1 and 6 or the power rollers 8 and 8, the members 1, 6, and 8 may increase in size, which is not desirable to realize a decrease in size of the apparatus.
Meanwhile, in order to prevent the above-described problems, for instance, Japanese Patent Unexamined Publications JP-A-2002-39306, JP-A-2003-207009, JP-A-2003-278869 and JP-A-2003-343675 disclose a technique in which a plurality of concave grooves having a depth in the range of 0.1 μm to 8 μm are formed in the whole one-side surfaces of the disks 1 and 6 or the peripheral surface (traction surface) of the power roller 8 so as to intersect each other. When such a technique is adopted, it is possible to improve a traction coefficient of the rolling contact area, and thus it is thought that large torque can be transmitted by a small pressing force compared with a structure without such concave grooves.
In this case, when a traction coefficient is largely improved to obtain a high capacity (an increase in allowable transmission torque) with such a structure, for instance, the depth of the concave groove may be set to large (deep).
However, when the depth of the concave grooves is set to large (deep), it is difficult to ensure durability of a working tool for forming the concave grooves, and thus a manufacture cost may increase. In addition, when the concave grooves are formed by, for instance, a rolling process, a traction surface corresponding to the surface to be processed may be broken or bending fatigue thereof may deteriorate. On the contrary, for instance, when the concave grooves are formed in both the one-side surfaces of the disk 1 and 6 in the axial direction and the peripheral surface of the power roller 8, it is possible to remarkably improve a traction coefficient even when the depth of the concave grooves is not extremely large (deep). However, when the concave grooves are formed in both surfaces of the disks 1 and 6 and the power roller 8, durability of the disks 1 and 6 or the power roller 8 may not be ensured just by simply forming the concave grooves in the surface (traction surface). Regarding this point, a description thereof will be carried out hereinafter.
That is, in the structure disclosed in the JP-A-2002-39306, JP-A-2003-207009, JP-A-2003-278869 and JP-A-2003-343675, the plurality of concave grooves are formed in the peripheral surfaces of the power rollers 8 or the one-side surfaces of the disks 1 and 6 in the axial direction so as to have a spiral shape or a concentric shape about the central shaft (rotation shaft) of the member. Here, for instance, as shown in FIG. 11, it may be supposed that concave grooves 15 and 15 with a concentric shape are formed in a peripheral surface 18 of the power roller 8 and one-side surfaces 3 and 7 of disks 1 and 6. In addition, FIG. 11 is a schematic view in which the concave grooves 15 and 15 are enlarged for the convenience of understanding the formation state of the concave grooves 15 and 15 (a relationship between a groove width and a groove pitch P of the concave grooves 15 is larger than an actual relationship). In fact, the depth of the concave grooves 15 and 15 is in the range of 0.1 to 8 μm or so, the groove width thereof is in the range of 10 to 500 μm or so, and the groove pitch thereof is in the range of 25 to 500 μm. Then, in a structure in which the concave grooves 15 and 15 are formed into a concentric shape, a contact area of the rolling contact area between the one-side surfaces 3 and 7 of the disks 1 and 6 and the peripheral surface 18 of the power roller 8 may not be sufficiently ensured in accordance with a transmission gear ratio between the disks 1 and 6, that is, an inclination angle of the power rollers 8 and 8.
That is, as described above, in the structure in which the concave grooves 15 and 15 are formed into a concentric shape, the concave grooves 15 and 15 are opposed to each other in parallel in the rolling contact area. Here, as shown in FIG. 12A which schematically showing a contact state of the rolling contact area, when the concave grooves 15 and 15 are opposed to each other having the same positional relationship with each other, a problem that a substantial contact area of the rolling contact area (a total sum of a contact area in the rolling contact area other the concave grooves 15 and 15) becomes smaller than a necessary area does not occur.
However, as shown in FIG. 12B, since a positional relationship between the concave grooves 15 and 15 is deviated in accordance with the transmission gear ratio between the disks 1 and 6, a substantial contact area in the rolling contact area may decrease. In addition, although it is not shown in the drawing, even when the concave grooves with a spiral shape are formed in the traction surface, since the concave grooves in the rolling contact area are opposed to each other in parallel, the substantially same problem as that of the concave grooves 15 and 15 with the concentric shape may occur (the substantial contact area may decrease for the same reason because the concave grooves are opposed to each other with slightly different parallelism).
Then, when the contact area becomes small in this way, a surface pressure of the rolling contact area increases, and thus in a remarkable state, a metal contact may occur between the traction surfaces in the rolling contact area. The transmission gear ratio between the disks 1 and 6 changes in accordance with an operation state. However, for instance, during a constant-speed operation, the operation is carried out in a state that the transmission gear ratio is constant. Then, in such a state, when the contact area in the rolling contact area becomes small, durability of the disks 1 and 5 or the power rollers 8 and 8 may deteriorate, which is not desirable.